The soil microbe Bacillus thuringiensis (B.t.) is a Gram-positive, spore-forming bacterium characterized by parasporal crystalline protein inclusions. These often appear microscopically as distinctively shaped crystals. The proteins are highly toxic to pests and specific in their activity. The toxin genes have been isolated and sequenced, and recombinant DNA-based B.t. products produced and approved. In addition, with the use of genetic engineering techniques, new approaches for delivering B.t. endotoxins to agricultural environments are under development, including the use of plants genetically engineered with endotoxin genes for insect resistance and the use of stabilized intact microbial cells as B.t. endotoxin delivery vehicles (Gaertner, F. H., L. Kim [1988] TIBTECH 6:S4-S7). Thus, isolated B.t. endotoxin genes are becoming commercially valuable.
Over the past 30 years, commercial use of B.t. pesticides has been largely restricted to a narrow range of Lepidopteran (caterpillar) pests. Preparations of the spores and crystals of B. thuringiensis subsp. kurstaki have been used for many years as commercial insecticides for lepidopteran pests. In recent years, however, investigators have discovered B.t. pesticides with specificities for a much broader range of pests.
Other varieties of B.t., namely israelensis and san diego, have been used commercially to control insects of the orders Diptera and Coleoptera, respectively (Gaertner, F. H. [1989] "Cellular Delivery Systems for Insecticidal Proteins: Living and Non-Living Microorganisms," in Controlled Delivery of Crop Protection Agents, R. M. Wilkins, ed., Taylor and Francis, New York and London, 1990, pp. 245-255).
Recently, many new subspecies of B.t. have been identified, and many genes responsible for active .delta.-endotoxin proteins have been isolated (Hofte, H., H. R. Whiteley [1989] Microbiological Reviews 52(2):242-255). Hofte and Whiteley classified 42B.t. crystal protein genes into 14 distinct genes, grouped into 4 major classes based on amino-acid sequence and host range. The classes were CryI (Lepidoptera-specific), CryII (Lepidoptera- and Diptera-specific), CryIII (Coleoptera-specific), and CryIV (Diptera-specific). The discovery of strains specifically toxic to protozoan pathogens, animal-parasitic liver flukes (Trematoda), ants, or mites (Acari) has broadened the potential B.t. product spectrum even further. With activities against unique targets, these novel strains retain their very high biological specificity, and nontarget organisms remain unaffected. The availability of a large number of diverse B.t. toxins may also enable farmers to adopt product-use strategies that minimize the risk that B.t.-resistant pests will arise.
Thus, many different B.t. toxins are now known. However, to date, the method for isolating the responsible toxin genes has been a slow empirical process. That is, for a given B.t. isolate, there is currently no rapid systematic method for identifying the responsible toxin genes or for predicting the activity of a given B.t. isolate. Currently, a given B.t. isolate must first be placed through a tedious series of bioassays to determine its spectrum of insecticidal activity, and subsequently an attempt is made to isolate the genes responsible for the observed insecticidal activity, generally through the nonsystematic use of mixed or randomly selected oligomeric probes.
The subject invention eliminates some of the empirical nature of finding certain B.t. insecticidal protein toxin genes. Although the process is still highly unpredictable, this invention facilitates expedient identification of potentially new commercially valuable insecticidal endotoxin genes.
Although a recent report of such methods has appeared (see Carozzi, N. B., V. C. Kramer, G. W. Warren, S. Evola, G. Koziel [1991] Appl. Env. Microbiol. 57(11):3057-3061), this report postdates our original filing date and does not disclose or suggest the specific probes of the subject invention. Also, EP 0 358 557 AZ discloses an amino acid sequence which has sequence similarity to SEQ ID NO. 1, below, but it is 30% longer.